Effects of preheating treatment on thermal property and adhesion performance of soy protein isolates

The objective of this research was to study the effects of preheating treatment and thermal-setting temperature on the thermal properties and adhesion performance of esterified and cross-linked soy protein isolates. Preheating treatment was achieved by heating a soy protein isolate suspension (5% solid) for 20 min at 60, 80, 110 or 130°C. Thermal-setting temperatures of 130, 160, 190 and 220°C were achieved by adjusting the temperature of the hot press. Differential scanning calorimetry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used to determine changes in the protein structure before and after preheating treatment. Preheating treatment had a significant effect on protein structure and adhesion performance. Adhesion strength of control and esterified soy protein isolates reached maximum at 80°C preheating temperature. Severe preheating (over 110°C) caused complete denaturation of proteins and loss of their native structure and was, therefore, detrimental to adhesion performance. Thermal-setting temperature also had a significant effect on protein structure and wet strength of the soy protein isolates. Wet adhesion strength of unmodified, esterified, and cross-linked soy protein isolates increased by 170%, 128% and 80%, respectively, as the thermal-setting temperature increased from 130 to 220°C.